Hidden features of WPF and XAML?

Question

Multibinding (combined with StringFormat):

<TextBlock>
  <TextBlock.Text>
    <MultiBinding StringFormat="{}{0}, {1}">
      <Binding Path="LastName" />
      <Binding Path="FirstName" />
    </MultiBinding>
  </TextBlock.Text>
</TextBlock>

There is also PresentationTraceSources.TraceLevel trick to debug what is going on with bindings in any particular scenario. All you have to do is to reference System.Diagnostics namespace in WindowsBase assembly

xmlns:sd="clr-namespace:System.Diagnostics;assembly=WindowsBase"

and then add following to the binding expression:

<TextBlock Text="{Binding Message, sd:PresentationTraceSources.TraceLevel=High}"  />

Log will be like this:

System.Windows.Data Warning: 52 : Created BindingExpression (hash=5923895) for Binding (hash=7588182)
System.Windows.Data Warning: 54 :   Path: 'Message'
System.Windows.Data Warning: 56 : BindingExpression (hash=5923895): Default mode resolved to OneWay
System.Windows.Data Warning: 57 : BindingExpression (hash=5923895): Default update trigger resolved to PropertyChanged
System.Windows.Data Warning: 58 : BindingExpression (hash=5923895): Attach to System.Windows.Controls.TextBlock.Text (hash=65248697)
System.Windows.Data Warning: 63 : BindingExpression (hash=5923895): Resolving source 

3.5sp1 introduced TargetNullValue to bindings. This will set the bound property to Null if the value is entered and if your property is Null it will display this value.

<TextBox Text="{Binding Total, TargetNullValue=$0.00}" />

3.5sp1 introduced StringFormat into binding expressions, e.g.

<TextBox Text="{Binding Date, StringFormat='{}{0:MM/dd/yyyy}'}" />